1. Field of the Invention
The present invention relates to an apparatus for manufacturing semiconductor and more particularly, to a cold wall chemical vapor deposition apparatus and a cleaning method of a chamber for the same.
2. Discussion of the Related Art
A development for a new material has been actively performed in the field and diverse large-scale integrated circuit (LSI) such as ultra large-scale integrated circuit (ULSI) has been developed thanks to a rapid growth of the new material development. That is, because the new material for forming thin films such as an insulating layer, a semi-conductor layer and a conductor layer, which constitute a semi-conductor device, has been developed widely in the field, the large-scale integrated circuit (LSI) such as the ultra large-scale integrated (ULSI) circuit is available now. As the society proceeds to the information age, an electric goods, which has a low weight, a small size and a thin dimension, has been required in the field. Because structural elements of the semi-conductor device requires a high reliability, a thin film forming method, which satisfies conditions such as a uniform deposition, a superior step coverage and a complete removal of particles, is required. Accordingly, many thin film deposition methods such as a chemical vapor deposition (CVD) method and a physical vapor deposition (PVD) method have been developed in the field.
Because the chemical vapor deposition method has many advantages compared with other deposition methods, it has usually been used for a manufacturing method of the semi-conductor device. A selective epitaxial growth (SEG) method in which a thin film is formed by growing a crystal grain selectively on a particular region of a substrate using the chemical vapor deposition method, is used in a manufacturing process for an integrated circuit such as the large-scale integrated circuit (LSI) or above the large scale integrated circuit (LSI). The selective epitaxial growth method is now used particularly in the integrated circuit manufacturing process in which an insulating film such as silicon oxide (SiO2) or silicon nitride (Si3N4) is formed in line patterns on a silicon substrate and a silicon film is selectively accumulated in an exposed region of the silicon substrate.
FIG. 1 is a schematic plan view of a conventional hot wall chemical vapor AFT deposition apparatus. The hot wall chemical vapor deposition apparatus 2 is one of apparatuses that perform the selective epitaxial growth process of the silicon. The hot wall chemical vapor deposition apparatus 2 includes a chamber 4 and a wall of the chamber 4 is heated by three-zone resistance heater 6. A forming process of the silicon thin film on a wafer in the hot wall chemical vapor deposition apparatus is as follows. First, a wafer is loaded into the chamber 4 of the hot wall chemical vapor deposition apparatus 2 and subsequently source gas, which will grow into the thin film, is supplied into the chamber 4. The chamber 4 is then heated by the three-zone resistance heater 6. The silicon thin film is subsequently formed on the wafer by growing silicon crystals on the wafer under high temperature condition in the chamber 4. At this time, because the wall of the chamber 4 is heated to a high temperature, the source gas is undesirably deposited thin on an inner surface of the chamber wall. The deposition of the source gas on the inner surface of the chamber 4 has disadvantages as followings. First, it increases a loss of material due to an unintentional deposition. Second, a rupture of the chamber 4 may occur when the chamber 4 is cooled down after a completion of the depositing process because of a contraction ratio difference between the chamber wall and the thin film deposited on the chamber wall. Third, because interior condition of the chamber 4 is under high temperature, the source gas such as silane (SiH4) or disilane (Si2H6), which is deposited on the chamber inner wall, is actively gasified and thus decreases a growing speed of the silicon crystal on the insulating film such as silicon oxide (SiO2) or silicon nitride (Si3N4). For this reason, it is difficult to grow the silicon crystal over 500 Å under the condition like this. Therefore, a cold wall chemical vapor deposition apparatus has been suggested to overcome these problems.
The cold wall chemical vapor deposition apparatus includes a chamber and a susceptor in the chamber. The susceptor includes a heater in it. After an interior of the chamber is vacuumed, the heater of the susceptor is turned on to heat up the susceptor. When the susceptor is heated by the heater, the wafer on the susceptor is also heated indirectly.
FIG. 2 is a cross-sectional view illustrating a conventional cold wall chemical vapor deposition apparatus. The conventional cold wall chemical vapor deposition apparatus 20 includes a chamber 22, exhaust units 28 and 30 and a gas supply unit 24. The chamber 22 is a place where the thin film deposition is performed and is electrically grounded. The susceptor 36 is positioned in the chamber 22 and the wafer 34, which is formed of silicon material, is loaded on the susceptor 36. The exhaust units 28 and 30 are for exhausting the air in the chamber 22. The gas supply unit 24 is for storing the source gas and providing the source gas into the chamber 22. The exhaust units 28 and 30 consist of a first exhaust unit 30 and a second exhaust unit 28. The first exhaust unit 30 is for whole region of the interior of the chamber 22 and the second exhaust unit 28 is mainly for a surrounding of the susceptor 36. An ultra-high vacuum (UHV) exhaust system, which uses a turbo molecular pump, is included in the exhaust units 28 and 30 and thus the interior of the chamber 22, particularly the surrounding of the susceptor 36 where the thin film deposition process is performed, comes to be in ultra high vacuum state. The susceptor 36 is fixed to a bottom of the chamber 22 and the wafer 34 on which the thin film is to be deposited is put on the susceptor 36. The susceptor 36 is generally made of silicon material, which is also a material for the wafer, such as graphite or silicon carbide (SiC), for example, not to damage the wafer 34. The susceptor 36 includes the heater 37 and an internal electrode 38. A heat reflector 32 is formed over the susceptor 36 with same material as the thin film on the wafer 34. The heat reflector 32 reflects a radiant heat that is emitted from the wafer 34 and the susceptor 36 back to the wafer 34 to improve a heating efficiency for the wafer 34 in the chamber 22. The thin film material is undesirably deposited on the heat reflector 32 as well as on the wafer during the thin film depositing process, and accordingly the heat reflector 32 is formed of the same material as the thin film material on the wafer 34 to prevent the thin film material deposited on the heat reflector 32 from being easily separated away from the heat reflector 32. A radio-frequency (RF) electrode 33, which serves to form an electric field between the radio-frequency (RF) electrode 33 and the internal electrode 38 by a radio-frequency (RF) power supply 35, is formed in the heat reflector 32. The cold wall chemical vapor deposition apparatus 20 may further include a refrigerating device to cool down the wall of the chamber 22.
The thin film deposition process in the cold wall chemical vapor deposition apparatus will be described hereinafter with reference to FIG. 2 and FIG. 3. The wafer 34 is carried into the chamber 22 from outside through a slot valve 26 and then is loaded onto the susceptor 36. The interior state of the chamber 22 subsequently becomes an ultra high vacuum state of 10−8 Torr by the first exhaust unit 30 and the second exhaust unit 28. Because the susceptor 36 was already heated by the heater 37 before the loading of the wafer on the susceptor 36, the wafer 34 is heated up to a certain temperature, usually about 700° C., and then the source gas is supplied into the chamber 22 through the gas supply unit 24. At this time, the interior of the chamber 22 is under the ultra high vacuum state and accordingly the source gas reaches the wafer 34 by being scattered in the chamber 22. Because the wafer 34 was heated up by the heater 37 in the susceptor 36, the source gas is resolved into its components as it reaches a surface of the wafer 34 and then deposited on the wafer 34. A line pattern is usually formed on the surface of the wafer 34 using the insulating film such as silicon oxide (SiO2) film or silicon nitride (Si3N4) film, for example. The surface of the wafer 34 includes a surface region where the silicon, which is the material for the wafer 34, is exposed to the air and a surface region where the insulating film such as silicon oxide (SiO2) film or silicon nitride (Si3N4) film is exposed to the air. Because the reaction rate on the silicon surface is much faster than the reaction rate on the silicon oxide (SiO2) film surface or the silicon nitride (Si3N4) film surface, the silicon is selectively accumulated only on the silicon surface of the wafer 34.
The cold wall chemical vapor deposition apparatus 20 in which the silicon crystals are selectively grown on the surface of the wafer 34, has a few disadvantages as followings. First, the thin film may not be formed on the surface of the wafer uniformly due to an irregular heating of the wafer 34. That is, the cold wall chemical vapor deposition apparatus includes only the heater 37 in the susceptor 36 for its heating source and accordingly there occurs a temperature difference between a top surface of the wafer 34 and a bottom surface of the wafer 34. This temperature difference between the top surface and the bottom surface causes an irregular temperature distribution through the whole wafer 34 and thus causes a different silicon crystal growth depending on a region of the wafer 34. Because a deposition speed of the source gas on the wafer surface is in proportion to the temperature of the wafer 34, the different temperature distribution of the wafer 34 causes that the thin film is not formed uniformly on the wafer 34. If other elements are already formed on the wafer 34, the irregular deposition phenomenon becomes more serious because of a step of other elements. For example, a deposition speed of polysilicon shows a 2.0 to 2.5 percent difference when there is a temperature difference of 1° C. FIG. 3 is a graph illustrating a temperature difference between the wafer 34 and a cold wall in a conventional cold wall chemical vapor deposition apparatus 20. As shown in the figure, a temperature of the cold wall is usually maintained at about 20° C. and a temperature of the susceptor 36 is usually maintained at about 700° C. Accordingly, there is a temperature difference of 25° C. between the top surface and the bottom surface of the wafer 34, which contacts the susceptor 36.
Another disadvantage of the cold wall chemical vapor deposition apparatus 20 is that the thin film may also be formed undesirably on the heat reflector 32 and then separated away from the heat reflector 32 serving as a contaminating material. That is, if a thickness of the thin, which is deposited on the heated reflector 32 during a repeated deposition process, becomes thick, the deposited thin film on the heat reflector 32 comes to be separated away from the heat reflector 32 due to its weight and floats around as particles in a shape of dust in the chamber 22. If these particles of the separated thin film sticks to the elements on the wafer 34, they act as impurities and thus lower a reliability of the elements of the wafer 34.